Digital current mode controller

1. A digital current-mode controller for a DC-DC converter, the controller comprising: a digital current reference; and a current loop compensator adapted to receive a digital current error signal derived from a digital current sample sensed from the DC-DC converter and the digital current reference and to generate a duty-cycle command, wherein the current loop compensator generates the duty-cycle command by adding a steady-state component of the duty-cycle generated by low-pass filtering the duty cycle command and a signal dependent on the digital current error signal.

2. A digital current-mode controller according to claim 1 wherein the digital current reference comprises a constant reference value.

3. A digital current-mode controller according to claim 1 wherein the digital current reference is generated by a voltage loop compensator adapted to receive a digital voltage error value.

4. A digital current-mode controller according to claim 3 further comprising a voltage A/D converter adapted to provide the digital voltage error value.

5. A digital current-mode controller according to claim 1 wherein the current loop compensator comprises a moving-average low-pass filter.

6. A digital current-mode controller according to claim 1 wherein the digital current sample tracks the digital current reference with a delay of one switching cycle.

8. A digital current-mode controller according to claim 7 wherein the current compensator gain k i =L/(T s V g ), in which L is an inductor value of the DC-DC converter, V g is an input voltage to the DC-DC converter, T s is a switching period of the DC-DC converter.

9. A digital current-mode controller according to claim 1 wherein the duty cycle command comprises a relatively larger resolution than the digital current sample.

10. A digital current-mode controller according to claim 1 further comprising a current analog-to-digital (A/D) converter adapted to provide the digital current sample.

11. A digital current-mode controller according to claim 10 wherein the current A/D converter comprises a differential delay line configuration.

12. A digital current-mode controller according to claim 1 further comprising a digital pulse-width-modulator adapted to provide a gate drive signal for a switch of a DC-DC converter in response to the duty-cycle command.

13. A switched-mode DC-DC regulator comprising: a switched-mode DC-DC converter comprising an input voltage terminal and an output voltage terminal, the switched-mode DC-DC converter comprising a switch; a current analog-to-digital converter adapted to provide a digital sensed current value corresponding to an analog current value in the DC-DC converter; a digital current reference; and a current loop compensator adapted to receive a digital current error signal derived from the digital sensed current value and the digital current reference, and to generate a duty-cycle command, wherein the current loop compensator generates the duty-cycle command by adding (i) a steady-state component of the duty-cycle generated by low-pass filtering the duty cycle command and (ii) a signal dependent on the digital current error signal.

14. A switched-mode DC-DC regulator according to claim 13 further comprising: a voltage analog-to-digital converter adapted to provide a digital voltage error signal based upon an output voltage of the switched-mode DC-DC voltage regulator; and a voltage loop compensator adapted to determine the digital current reference based upon the digital voltage error signal.

15. A switched-mode DC-DC regulator according to claim 14 wherein the voltage analog-to-digital converter is adapted to sense an analog voltage of the switched-mode DC-DC converter, compare the sensed voltage to a reference voltage, and provide the digital voltage error signal.

16. A switched-mode DC-DC regulator according to claim 13 further comprising a digital pulse-width-modulator adapted to provide a pulse-width-modulated control signal to control the operation of the switch of the switched-mode DC-DC converter.

17. A switched-mode DC-DC regulator according to claim 13 wherein the switched-mode DC-DC converter comprises a buck converter.

18. A switched-mode DC-DC regulator according to claim 13 wherein the current analog-to-digital converter comprises an offset.

19. A switched-mode DC-DC regulator according to claim 18 wherein the offset comprises one-half of a least significant bit of the digital sensed current value.

20. A switched-mode DC-DC regulator according to claim 18 wherein the offset is added to the digital sensed current value where an oscillation cycle exceeds a predetermined threshold and no offset is added where the oscillation cycle does not exceed the predetermined threshold.

21. A method of generating a duty-cycle command for a DC-DC converter, the method comprising: receiving a digital current reference; receiving a digital current sample sensed from the DC-DC converter; generating a digital current error signal derived from the digital current reference and the digital current sample; and providing a current compensator to generate a duty-cycle command by adding (i) a steady-state component of the duty-cycle command generated by low-pass filtering the duty cycle command and (ii) a signal dependent on the digital current error signal.

22. A method according to claim 21 wherein the low-pass filter comprises a moving-average low-pass filter.